Spinal cord injury (SCI) often damages not only white matter axon tracts that carry signals to and from the brain, but also the central gray matter, causing segmental losses of interneurons and motor neurons. Transplantation of neural stem cells or neural progenitors not only potentially replaces lost neurons and glia, but could also serve as a functional relay between spinal cord segments that are disconnected by injury. Our preliminary data provide strong support for this functional relay hypothesis, showing grafted embryonic neurons support formation of functional electrophysiological relays across sites of complete spinal transection, resulting in behavioral recovery; spinal re- transection abolished all recovery. The proposed studies will determine whether extrinsic neurotrophins promote host supraspinal axon regeneration and re-innervation of grafted embryonic neurons to further strengthen formation of functional relays after SCI. In addition, we will examine mechanisms underlying functional relay formation and identify genes responsible for corticospinal tract axonal regeneration, using BAC-TRAP translational profiling. Lastly, we will transfer advances from rat embryonic spinal cord neuronal progenitor work to human embryonic stem (ES) cell approaches. This work will reveal whether extrinsic stimulation of neural systems after SCI can enhance supraspinal axonal regeneration and form graft-mediated neuronal relays that facilitate functional recovery. Further, this model system will provide a rich opportunity for identifying molecular mechanisms underlying axonal regeneration. The goals of this research are directly and highly relevant to the VA patient care mission.